A high-frequency semiconductor device has a high-frequency semiconductor element such as a field effect transistor (FET) and a matching device in a high-frequency package.
A matching device has a transmission line and a plurality of chip capacitors. The transmission line is provided on a surface of a dielectric substrate. The chip capacitor is composed of another dielectric substrate and electrodes which are respectively provided on the surface and the rear face of this dielectric substrate. And, the dielectric substrate on which the transmission line is formed and the chip capacitors are mounted on a sheet of a metal plate, the transmission line and the chip capacitors are electrically connected, respectively, and thereby the matching device is made up. In addition, the dielectric substrate on which the transmission line is formed and the chip capacitors are mounted on the metal plate using gold tin (AuSn).
In a matching device like this, if a circuit is composed of distributed constant, a circuit size becomes large and a circuit area of the matching circuit also becomes large, and thereby the area which the matching device occupies also becomes large. Since the dielectric substrate on which the transmission line is formed and the chip capacitors are different components, the number of the components required for composing the matching device is increased, and thereby after all the area which the matching device occupies becomes large.
In case that the area which the matching circuit occupies is large, a high-frequency package which encloses the matching circuit becomes large. The high frequency package has a problem that it cannot be made large without restriction because a resonance frequency is decided according to the wavelength to deal with. Moreover, from the difference between the coefficient of linear thermal expansion of the material of the package, and the coefficient of linear thermal expansion of the material of the matching device, after attaching the matching device to the package, a problem that the crack of the matching device and peeling of the matching device generates. The rate which the crack and peeling generate becomes high in proportion to the increase in area.
In addition, even in the case of a high-frequency device other than a matching device, in a conventional high-frequency device having a transmission line provided on a surface of a dielectric substrate and a plurality of chip capacitors, the number of components is large (Refer to JP, P2002-135011A). For this reason, the conventional high-frequency device has the same problem as the matching device.